Physical Description

Diagnostic Description

Description

Worldwide in tropical and temperate seas. Diverse group of eels with large mouths with numerous teeth; often with fanglike (canine) teeth. Dorsal fin origin usually before the gill openings; median fins confluent with caudal fin; no pelvic and pectoral fins. Gill openings as small roundish lateral openings. Head with 1-3 lateral line pores; absent on body. Scaleless. Recorded maximum length 3.0 m. Some morays cause ciguatera fish poisoning. A skin toxin was noted in an Indo-Pacific moray eel. Adults benthic, generally in shallow water among rocks and coral heads; many species are more active at night and hide in holes and crevices during the day. Vicious reputation is undeserved, although some species will bite if provoked. Feed mainly on crustaceans and small fishes. Larvae (leptocephali) epipelagic, widespread and abundant.

The smallest moray is likely Snyder's moray (Anarchias leucurus), which attains a maximum length of 11.5 cm (4.5 in),[3] while the longest species, the slender giant moray (Strophidon sathete) reaches up to 4 m (13 ft).[4] The largest in terms of total mass is the giant moray (Gymnothorax javanicus), which reaches 3 m (9.8 ft) in length and 30 kg (66 lb) in weight.[5]

The dorsal fin extends from just behind the head along the back and joins seamlessly with the caudal and anal fins. Most species lack pectoral and pelvic fins, adding to their serpentine appearance. Their eyes are rather small; morays rely on their highly developed sense of smell, lying in wait to ambush prey.

The body is generally patterned. In some species, the inside of the mouth is also patterned. Their jaws are wide, framing a protruding snout. Most possess large teeth used to tear flesh or grasp slippery prey items. A relatively small number of species, for example the snowflake moray (Echidna nebulosa) and zebra moray (Gymnomuraena zebra), primarily feed on crustaceans and other hard-shelled animals, and they have blunt, molar-like teeth suitable for crushing.[6]

Moray eel jaw anatomy

Moray eels' heads are too narrow to create the low pressure most fishes use to swallow prey. Quite possibly because of this, they have a second set of jaws in their throat called pharyngeal jaws, which also possess teeth (like tilapia). When feeding, morays launch these jaws into the mouth, where they grasp prey and transport it into the throat and digestive system. Moray eels are the only animals that use pharyngeal jaws to actively capture and restrain prey.[7][8][9]

Morays secrete a protective mucus over their smooth, scaleless skin, which in some species contains a toxin. They have much thicker skin and high densities of goblet cells in the epidermis that allows mucus to be produced at a higher rate than in other eel species. This allows sand granules to adhere to the sides of their burrows in sand-dwelling morays,[10] thus making the walls of the burrow more permanent due to the glycosylation of mucins in mucus. Their small, circular gills, located on the flanks far posterior to the mouth, require the moray to maintain a gap to facilitate respiration.

Reef-associated roving coralgroupers (Plectropomus pessuliferus) have been observed to recruit morays to join them in hunting for food. The invitation to hunt is initiated by head-shaking. The rationale for this joining of forces is the ability of morays to enter narrow crevices and flush prey from niches not accessible to groupers. This is the only known instance of interspecies cooperative hunting among fish. Cooperation on other levels, such as at cleaning stations, is well-known.[11][12]

Morays are frequently thought of as particularly vicious or ill-tempered animals. In truth, morays hide from humans in crevices and would rather flee than fight. They are shy and secretive, and attack humans only in self defense or mistaken identity. Most attacks stem from disruption of a moray's burrow (to which they do react strongly), but an increasing number also occur during hand feeding of morays by divers, an activity often used by dive companies to attract tourists. Morays have poor vision and rely mostly on their acute sense of smell, making distinguishing between fingers and held food difficult; numerous divers have lost fingers while attempting hand feedings, so the hand feeding of moray eels has been banned in some locations, including the Great Barrier Reef. The moray's rear-hooked teeth and primitive but strong bite mechanism also makes bites on humans more severe, as the eel cannot release its grip, even in death, and must be manually prised off. While the majority are not believed to be venomous, circumstantial evidence suggests a few species may be.[6]

Eels that have eaten certain types of toxic algae, or more frequently that have eaten fish that have eaten some of these algae, can cause ciguatera fish poisoning if eaten. Ciguatera fish poisoning is very dangerous and can kill.

Moray eels are cosmopolitan, found in both tropical and temperate seas, although the largest species richness is at reefs in warm oceans. Very few species occur outside the tropics or subtropics, and the ones that do only extend marginally beyond these regions. They live at depths to several hundred metres, where they spend most of their time concealed inside crevices and alcoves. While several species regularly are found in brackish water, very few species can be found in fresh water, for example, the freshwater moray (Gymnothorax polyuranodon) and the pink-lipped moray eel (Echidna rhodochilus).[13]